Violet vs Blueberry

How close are they?

ΔE 15.9, loose: different enough that you should pick on purpose. Blueberry is a little darker, more saturated, warmer than Violet.

Can I use Blueberry instead of Violet?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Blueberry is a little darker, more saturated, warmer than Violet.

Can I use Violet instead of Blueberry?

The same difference applies the other way round: Violet is a little lighter, more muted, cooler.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.